Retro-focus type wide angle lens system

ABSTRACT

A retro-focus type wide angle lens system comprises a negative first component located on the object side and including at least one negative meniscus lens; a positive intermediate second component consisting of one or two lens groups including at least one biconvex lens group and a rear third component which includes of four consecutive lenses including, in order, a positive meniscus first lens having a rear convex surface, a biconcave second lens, a positive meniscus third lens having a rear convex surface and a fourth positive lens; whereby the back focus of the total lens system is longer than the focal length, and satisfying the following conditions: 
     
         (1)d.sub.c0 &gt;  d.sub.c2 
    
     
         (2)|r.sub.c2 |≧ | r.sub.c3 | 
    
     
         (3)V.sub.c1 &gt; V.sub.c2 
    
     
         (4)d.sub.c0 &gt; d.sub.c4 
    
     wherein 
     r c2  and r c3  are the radius of curvature of the rear surface of the first lens of the third component and the radius of curvature of the front surface of the second lens of the third component, respectively; d c0  is the axial distance between the rear lens of the second component and the first lens of the third component; d c2  and d c4  are the axial distance between the first and second lenses of the third component and the axial distance between the second lens and the third lens; and 
     V c1  and V c2  are Abbe&#39;s Numbers of the first and second lenses of the third component.

BACKGROUND OF THE INVENTION

This invention relates to a wide angle lens of a retro-focus type, and more particularly to an objective lens adapted for use in a single lens reflex camera and having a back focus of a length greater than the focal length thereof.

Hitherto, the conventional type wide angle lens of this kind suffers from shortcomings in that the wider the angle of field, the more difficult will be the compensation of the various abberations, such that it is extremely difficult to provide a wide angle lens which has a large relative aperture of high brightness.

It is a principal object of the invention to provide a wide angle lens system of the retro-focus type for use in a photographic camera, said system having a field angle of 64° to 76°, a relative aperture of F/2.8 to F/2 and a back focus of a length of 1.06 to 1.32 times as long as the focal length, yet being highly compensated for the various abberations.

SUMMARY OF THE INVENTION

According to the present invention, there is provided a lens system of the retro-focus type, comprising: a first component which is located on the object side, has a negative refractive power and includes at least one negative meniscus lens; a second component which has a positive refractive power, consists of one or two lens groups including at least one biconvex lens group and is placed next to said first component; and a third component which consists of four lenses and is placed next to said second component, said four lenses consisting, in the order appearing from the object side of a positive meniscus first lens having the convex surface facing the image side, a biconcave second lens, a positive meniscus third lens having the convex surface facing the image side and a fourth positive lens; whereby the back focus of the total lens system is rendered longer than the focal length, while satisfying the following conditions:

    (1) d.sub.c0 > d.sub.c2

    (2) | r.sub.c2 | ≧ | r.sub.c3 |

    (3) V.sub.c1 > V.sub.c2

    (4) d.sub.c0 > d.sub.c4

wherein

r_(c2) and r_(c3) are radius of curvature of the curved surface, on the image side, of the first lens of the third component and radius of curvature of the curved surface, on the object side, of the second lens of the third component, respectively;

d_(c0) is an axial distance between the lens of the second component on the side nearest to the image and the first lens of the third component;

d_(c2) and d_(c4) are an axial distance between the first and second lenses of the third component and an axial distance between the second lens and the third lens; and

V_(c1) and V_(c2) are Abbe's Numbers of the first and second lenses of the third component.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing the construction of a first embodiment of the invention;

FIG. 2 is a diagram showing the construction of a second embodiment of the invention;

FIG. 3 is a diagram showing the construction of a third embodiment of the invention;

FIG. 4 is a diagram showing the construction of a fourth embodiment of the invention;

FIG. 5 to 8 are plots illustrating spherical aberrations, sine conditions, astigmatisms and distortions of the first to fourth embodiments, respectively; and

FIGS. 9 to 12 are coma of respective embodiments of the invention.

DETAILED DESCRIPTION OF THE INVENTION

According to the present invention, an objective lens system of a retro-focus type is divided into three components, i.e., a first to third component which are so referred to in the order from the object side or front to the image side or rear and in which, for achieving a back focus of a length greater than the focal distance, the first component A includes at least one negative meniscus lens, thereby presenting an improved diverging lens system. The lens system of the kind described includes one negative meniscus lens such as lens 1A in the first embodiment. However, if it is difficult to compensate the aberration created by the first component A by using the second component and above, the negative refractive power may be shared by the two negative lenses IA and II A as shown in the second embodiment, or one positive lens IIA (the third embodiment) or IA (the fourth embodiment) may be added to two negative lenses as shown in FIGS. 3 and 4, thereby reducing the aberration caused in the first component, while facilitating compensation of the aberrations created in the second component and after. However, in either case, it cannot be avoided that the distortion or coma is transmitted to the second component and after, without being compensated, when providing an improved diverging capability to the first component A.

For off-setting the aberration created in the aforesaid first component, there should be provided a second component B having a positive refractive power and consisting of one lens group including at least one biconvex lens group (The first, second and third embodiments) or two lens groups (fourth embodiment), whereby there is provided therein an aberration having an opposite sign to that of the aforesaid aberration created in the first component A for compensating same, after which the residual aberration therefrom will be finally compensated by the third component C, thereby obtaining a lens system having a wide angle, a large relative aperture and well compensated aberration.

The third component consists of four lenses, of which the first lens IC and the second lens IIC form a diverging lens group as a whole. In this respect, if the diverging lens group consists of a single lens IIC alone, a large coma aberration will result, whereby difficulties are encountered with the compensation of the chromatic aberration.

To cope with this, it may be considered to form the aforesaid diverging lens group by using the first positive lens, to which is adhered the second negative lens. This method enables the compensation of the chromatic aberration, but the coma remains uncompensated. According to the present invention, the first lens IC is spaced apart from the second lens IIC, with an air space being provided therebetween, and the air lens thus formed between the both lenses is deliberately utilized to eliminate the coma.

According to the present invention, the following relationship is established between the axial distance d_(c0) between the lens of the second component B, which is nearest to the image and the first lens of the third component C, and the axial distance d_(c2) between the first lens of the third component and the second lens IIC:

    d.sub.c0 > d.sub.c2

It should be noted that the above relationship, i.e., the first condition of the invention specifies the position of the first lens IC with respect to the positions of the second component B and third component C. If the aforesaid condition is not met, the coma compensation by means of the second lens IIC is difficult, while there is created a negative deviation in the astigmatism, thus resulting in shorter back focus.

According to a second condition of the system of the present invention, the following relationship is established between the radius of curvature r_(c2) of the rear surface of the first lens of the third component and the radius of curvature r_(c3) of the front surface of second lens IIC:

    |r.sub.c2 |≧ |r.sub.c3 |

The above second condition features the aforesaid air lens and enables the effective function thereof. Unless this condition is met, difficulties will be encountered in copensating coma, while the spherical aberration will result in a deviated position to the negative side.

According to a third condition of the invention, the following relationship is established between the Abbe's Number V_(c1) of the first lens IC of the third component and the Abbe's Number V_(c2) of the second lens IIC:

    v.sub.c1 > V.sub.c2

The above third condition provides for effective compensation of the longitudinal chromatic aberration and lateral chromatic aberration by means of the first lens IC and second lens IIC. If there is used an Abbe's Number which fails to meet this condition, then there will be lost the degree of freedom in selecting the Abbe's Number for the first and second components, such that it becomes difficult to compensate the longitudinal and lateral chromatic aberrations at the same time.

According to a fourth condition of the invention, the following condition is established between the aforesaid axial distance d_(c0) and the axial distance d_(c4) which is between the second lens IIC and the third lens IIIC of the third component C:

    d.sub.c0 > d.sub.c4

The fourth condition specifies the axial distance d_(c4). If the aforesaid condition is not met, then there will be increased negative distortion, while the coma will be negative, such that it becomes impossible to compensate coma throughout the entire field angles of the lens system.

Description will now be given of the first to fourth embodiments according to the present invention.

The first embodiment is a lens system consisting of six groups, i. e., six lenses, having a relative aperture of F/2.8 and a field angle of 2ω=64°.

The second embodiment is a lens system consisting of seven groups, i.e., seven lenses, having a relative aperture of F/2.8 and a field angle of 2ω=76°. The third and fourth embodiments are a lens system consisting of 8 groups, i.e., nine lenses and a lens system consisting of nine groups, i.e., 10 lenses respectively, both having a relative aperture of F/2.0 and a field angle of 2ω =76°.

The particulars of the first to fourth embodiments will be described hereinafter:Embodiment 1f = 1, 1:2.8, field angle 2ω = 64° back focus s' = 1.06Radius of Distance Refractive Abbe's Numbercurvature along axis index______________________________________rA1 = 2.6542 dA1 = 0.057 NA₁ = 1.5725 V_(A1) = 57.5rA2 = 0.5212 dBO = 0.3292rB1 = 0.6639 dB1 = 0.2149 N_(B1) = 1.6968 V_(B1) = 55.6rB2 = 2.3966 dCO = 0.1699rC1 = 0.9176 Dc1 = 0.07 N_(C1) = 1.6583 V_(C1) = 58.5rC2 = 0.8435 dC2 = 0.1326rC3 = 0.4272 dC3 = 0.0439 N_(C2) = 1.7006 V_(C2) = 30.1rC4 = 2.5205 dC4 = 0.045rC5 = 1.8428 dC5 = 0.067 N_(C3) = 1.7305 V_(C3) = 54.4rC6 = 0.5054 dC6 = 0.0029rC7 = 5.8432 dC7 = 0.068 N_(C4) = 1.6775 V_(C4) = 55.5rC8 = 1.0495 Σ0 d = 1.2004______________________________________

    Embodiment 2 f=-f =1:2/8,  field angle 2ω =0 76° back focus       s' = 1.31                                                                      Radius of Distance    Refractive Abbe's Number                                 curvature along axis  index                                                    ______________________________________                                         rA1 = 0.9483                                                                             dA1 = 0.08  N.sub.A1 = 1.6214                                                                         V.sub.A1 = 61.3                               rA2 = 0.5452                                                                             dA2 = 0.17                                                           rA3 = 1.2630                                                                             dA3 = 0.065 N.sub.A2 = 1.6204                                                                         V.sub.A2 = 60.3                               rA4 = 0.5736                                                                             dBO = 0.4145                                                         rB1 = 0.9542                                                                             dB1 = 0.31  N.sub.B1 = 1.7170                                                                         V.sub.B1 = 47.9                               rB2 = -1.8101                                                                            dCO = 0.1401                                                         rC1 = -5.2127                                                                            dC1 = 0.0767                                                                               N.sub.C1 = 1.7440                                                                         V.sub.C1 = 44.9                               rC2 = -1.1791                                                                            dC2 = 0.0984                                                         rC3 = -0.6112                                                                            dC3 = 0.1467                                                                               N.sub.C2 = 1.7552                                                                         V.sub.C2 = 27.6                               rC4 = 1.7625                                                                             dC4 = 0.0304                                                         rC5 =  -2.1584                                                                           dC5 = 0.085 N.sub.C3 = 1.7200                                                                         V.sub.C3 = 50.3                               rC6 = -0.5814                                                                            dC6 = 0.0032                                                         rC7 = 9.2635                                                                             dC7 = 0.07  N.sub.C4 = 1.6214                                                                         V.sub.C4 = 61.3                               rC8 = -1.8200                                                                            Σ d - 1.69                                                     ______________________________________                                    

    Embodiment 3                                                                   f = 1 1.2.0, field angle 2ω = 76° back focus s' = 1.32            Radius of  Distance   Refractive Abbe's Number                                 Curvature  along axis index                                                    ______________________________________                                         rA1 = 2.6524                                                                              dA.sub.1 = 0.1030                                                                         NA.sub.1 = 1.6031                                                                         VA.sub.1 = 60.7                               rA2 = 0.7652                                                                              dA.sub.2 = 0.3086                                                   rA3 = 1.6973                                                                              dA.sub.3 = 0.1441                                                                         NA.sub.2 = 1.6668                                                                         VA.sub.2 = 33.1                               rA4 = -147.9947                                                                           dA.sub.4 = 0.04                                                     rA5 = 1.3048                                                                              dA.sub.5 = 0.0959                                                                         NA.sub.3 = 1.6890                                                                         VA.sub.3 = 49.3                               rA6 = 0.5398                                                                              dB.sub.0 = 0.3153                                                   rB1 = 1.2986                                                                              dB.sub.1 = 0.2701                                                                         NB.sub.1 = 1.7050                                                                         VB.sub.1 = 54.8                               rB2 = -0.6026                                                                             dB.sub.2 = 0.1419                                                                         NB.sub.2 = 1.5190                                                                         VB.sub.2 = 57.3                               rB3 = -2.3600                                                                             dC.sub.0 = 0.1640                                                   rC1 = -1.2368                                                                             dC.sub.1 = 0.1100                                                                         NC.sub.1 = 1.5934                                                                         VC.sub.1 = 34.1                               rC2 = -0.8499                                                                             dC.sub.2 = 0.0862                                                   rC3 = -0.7622                                                                             dC.sub.3 = 0.1062                                                                         NC.sub.2 = 1.7847                                                                         VC.sub.2 = 25.7                               rC4 = 2.4184                                                                              dC.sub.4 = 0.0855                                                   rC5 = -1.8575                                                                             dC.sub.5 = 0.1007                                                                         NC.sub.3 = 1.7530                                                                         VC.sub.3 = 52.4                               rC6 = -0.7447                                                                             dC.sub.dC.sub.6 = 0.0067                                            rC7 = 5.1620                                                                              dC.sub.7 = 0.1950                                                                         NC.sub.4 = 1.7050                                                                         VC.sub.4 = 54.8                               C8 = -1.4574                                                                              Σd = 2.2729                                                   ______________________________________                                    

    Embodiment 4                                                                   f = 1, 1:2, field angle 2ω = 76°, back focus s' = 1.31            Radius of  Distance   Refractive Abbe's Number                                 curvature  along axis index                                                    ______________________________________                                         rA.sub.1 = 8.9525                                                                         dA.sub.1 = 0.135                                                                          NA.sub. 1 = 1.6935                                                                        VA.sub.1 = 53.4                               rA.sub.2 = -26.3137                                                                       dA.sub.2 = 0.004                                                    rA.sub.3 = 1.6630                                                                         dA.sub.3 = 0.06                                                                           NA.sub.2 = 1.5168                                                                         VA.sub.2 = 64.0                               rA.sub.4 = 0.6306                                                                         dA.sub.4 = 0.1152                                                   rA.sub.5 = 1.4500                                                                         dA.sub.5 = 0.06                                                                           NA.sub.3 = 1.5168                                                                         VA.sub.3 = 64.0                               rA.sub.6 = 0.5848                                                                         dB.sub.0 = 0.2622                                                   rB.sub.1 = 1.8044                                                                         dB.sub.1 = 0.06                                                                           NB.sub.1 = 1.5168                                                                         VB.sub.1 = 64.0                               rB.sub.2 = 1.9818                                                                         dB.sub.2 = 0.0704                                                   rB.sub.3 = 0.9816                                                                         dB.sub.3 = 0.2676                                                                         NB.sub.2 = 1.6975                                                                         VB.sub.2 = 48.2                               rB.sub.4 = -1.2300                                                                        dB.sub.4 = 0.094                                                                          NB.sub.3 = 1.5231                                                                         VB.sub.3 = 58.6                               rB.sub.5 = -5.0777                                                                        dC.sub.0 = 0.195                                                    rC.sub.1 = -1.9893                                                                        dC.sub.1 = 0.1097                                                                         NC.sub.1 = 1.6200                                                                         VC.sub.1 = 36.3                               rC.sub.2 = -0.8138                                                                        dC.sub.2 = 0.086                                                    rC.sub.3 = -0.6430                                                                        dC.sub.3 = 0.1064                                                                         NC.sub.2 = 1.8052                                                                         VC.sub.2 = 25.4                               rC.sub.4 = 2.6269                                                                         dC.sub.4 = 0.05                                                     rC.sub.5 = -2.6680                                                                        dC.sub.5 = 0.1                                                                            NC.sub.3 = 1.7570                                                                         VC.sub.3 = 47.9                               rC.sub.6 = -0.7408                                                                        dC.sub.6 = 0.0067                                                   rC.sub.7 = 3.8156                                                                         dC.sub.7 = 0.18                                                                           NC.sub.4 = 1.7050                                                                         VC.sub.4 =  54.8                              rC.sub.8 = -1.3884                                                                        Σd 1.9629                                                     ______________________________________                                    

Tables 1, 2, 3 and 4 show Seidel's co-efficient of aberrations of the first to fourth embodiments. These are also shown in FIGS. 5 to 8.

In the aforesaid respective embodiment, rA_(i) (i = 1 to 6) represents the radius of curvature of the i th curved surface of the first component from the front or object side, rB_(j) (j = 1 to 5) represents the radius of curvature of the j th curved surface of the second component from the front or object side, and rC_(k) (k = 1 to 8) represents the radius of curvature of the k th curved surface of the third component from the front object side. On the other hand, dA_(i) _(') (i' = 1 to 5) represents the thickness of a lens and the axial distance between lenses of the first component A, dB_(j) _(') (j' = 0 to 4) represents the thickness of a lens and the axial distance between lenses of the second component B, and dC_(k) _(') (k' = 0 to 7) represents the axial distance between lenses and the thickness thereof of the third component C. Meanwhile, FIGS. 9 to 12 show the lateral aberration of the respective embodiment.

For information, the Seidel's co-efficient of aberrations of the aforesaid four embodiments are shown in Tables 1, 2, 3 and 4 below.

                                      Table 1                                      __________________________________________________________________________     (Embodiment 1)                                                                 Surface                                                                             Spherical                                                                            Coma  Astigmatism                                                                           Pepzval                                                                              Distortion                                            Aberration         Sum                                                    __________________________________________________________________________     A.sub.1                                                                             0.0124                                                                               0.0262                                                                               0.0556 0.1372                                                                               0.4085                                           A.sub.2                                                                             -7.3600                                                                              0.9980                                                                               -0.1353                                                                               -0.6985                                                                              0.1131                                           B.sub.1                                                                             10.4218                                                                              0.4130                                                                               0.0164 0.6185                                                                               0.0252                                           B.sub.2                                                                             1.4344                                                                               -1.1083                                                                              0.8563 0.1714                                                                               -0.7940                                          C.sub.1                                                                             -3.4903                                                                              1.7161                                                                               -0.8438                                                                               -0.4326                                                                              0.6276                                           C.sub.2                                                                             4.4284                                                                               -1.8624                                                                              0.7833 0.4706                                                                               -0.5273                                          C.sub.3                                                                             -10.6632                                                                             2.0990                                                                               -0.4131                                                                               -0.9643                                                                              0.2711                                           C.sub.4                                                                             -1.2716                                                                              -1.1737                                                                              -1.0833                                                                               -0.1634                                                                              -1.1508                                          C.sub.5                                                                             0.0828                                                                               0.2189                                                                               0.5786 -0.2291                                                                              0.9239                                           C.sub.6                                                                             3.7158                                                                               -0.5923                                                                              0.0944 0.8352                                                                               -0.1482                                          C.sub.7                                                                             -0.0000                                                                              0.0006                                                                               -0.0732                                                                               0.0691                                                                               0.5226                                           C.sub.8                                                                             3.8059                                                                               -0.7161                                                                              0.1347 0.3848                                                                               -0.0978                                          Σ                                                                             1.1163                                                                               0.0189                                                                               -0.0296                                                                               0.1989                                                                               0.1738                                           __________________________________________________________________________

                                      Table 2                                      __________________________________________________________________________     (Embodiment 2)                                                                 Surface                                                                             Spherical                                                                            Coma  Astigmatism                                                                           Pepzval                                                                              Distortion                                            Aberration         Sum                                                    __________________________________________________________________________     A.sub.1                                                                             0.2772                                                                               0.0755                                                                               0.0206 0.4041                                                                               0.1157                                           A.sub.2                                                                             -3.3309                                                                              0.5329                                                                               -0.0853                                                                               -0.7029                                                                              0.1261                                           A.sub.3                                                                             0.8003                                                                               0.2364                                                                               0.0698 0.3031                                                                               0.1102                                           A.sub.4                                                                             -9.3529                                                                              0.8024                                                                               -0.0688                                                                               -0.6675                                                                              0.0632                                           B.sub.1                                                                             10.9071                                                                              1.1726                                                                               0.1261 0.4376                                                                               0.0606                                           B.sub.2                                                                             1.9032                                                                               -1.0229                                                                              0.5498 0.2307                                                                               -0.4195                                          C.sub.1                                                                             -0.5497                                                                              0.4413                                                                               -0.3543                                                                               -0.0818                                                                              0.3502                                           C.sub.2                                                                             9.4730                                                                               -2.6026                                                                              0.7150 0.3618                                                                               -0.2959                                          C.sub.3                                                                             -18.6801                                                                             3.0119                                                                               -0.4856                                                                               -0.7039                                                                              0.1918                                           C.sub.4                                                                             -1.9008                                                                              -1.2835                                                                              -0.8667                                                                               -0.2441                                                                              -0.7501                                          C.sub.5                                                                             0.0142                                                                               0.0657                                                                               0.3045 -0.1939                                                                              0.5123                                           C.sub.6                                                                             8.8349                                                                               -0.7636                                                                              0.0660 0.7200                                                                               -0.0679                                          C.sub.7                                                                             -0.0342                                                                              0.0740                                                                               -0.1603                                                                               0.0414                                                                               0.2576                                           C.sub. 8                                                                            3.0687                                                                               -0.7127                                                                              0.1655 0.2106                                                                               -0.0874                                          Σ                                                                             1.4300                                                                               0.0274                                                                               -0.0038                                                                               0.1150                                                                               0.1668                                           __________________________________________________________________________

                                      Table 3                                      __________________________________________________________________________     (Embodiment 3)                                                                 Surface                                                                             Spherical                                                                            Coma  Astigmatism                                                                           Pepzval                                                                              Distortion                                            Aberration         Sum                                                    __________________________________________________________________________     A.sub.1                                                                             0.0126                                                                               0.0218                                                                               0.0379 0.1418                                                                               0.3121                                           A.sub.2                                                                             -2.1203                                                                              0.6325                                                                               -0.1887                                                                               -0.4916                                                                              0.2029                                           A.sub.3                                                                             0.8991                                                                               0.1120                                                                               0.0140 0.2357                                                                               0.0311                                           A.sub.4                                                                             -0.0004                                                                              -0.0044                                                                              -0.0434                                                                               0.0027                                                                               -0.4038                                          A.sub. 5                                                                            0.3826                                                                               0.1239                                                                               0.0401 0.3386                                                                               0.1226                                           A.sub.6                                                                             -10.7381                                                                             1.5679                                                                               -0.2289                                                                               -0.7557                                                                              0.1438                                           B.sub.1                                                                             4.4900                                                                               0.5288                                                                               0.0623 0.3184                                                                               0.0448                                           B.sub.2                                                                             3.9824                                                                               -1.3745                                                                              0.4744 0.1192                                                                               -0.2049                                          B.sub.3                                                                             1.0484                                                                               -0.7359                                                                              0.5166 0.1448                                                                               -0.4642                                          C.sub.1                                                                             -2.3071                                                                              1.1285                                                                               -0.5520                                                                               -0.3011                                                                              0.4173                                           C.sub.2                                                                             6.9709                                                                               -2.1301                                                                              0.6509 0.4382                                                                               -0.3328                                          C.sub.3                                                                             -7.7568                                                                              2.0291                                                                               -0.5308                                                                               -0.5769                                                                              0.2898                                           C.sub.4                                                                             -1.1461                                                                              -0.8854                                                                              -0.6840                                                                               -0.1818                                                                              -0.6688                                          C.sub.5                                                                             0.0003                                                                               0.0085                                                                               0.2480 -0.2313                                                                              0.4891                                           C.sub. 6                                                                            2.8015                                                                               -0.5032                                                                              0.0904 0.5768                                                                               -0.1199                                          C.sub.7                                                                             -0.0004                                                                              -0.0016                                                                              -0.0062                                                                               0.0993                                                                               0.3714                                           C.sub. 8                                                                            4.1821                                                                               -0.5660                                                                              0.0766 0.2837                                                                               -0.0488                                          Σ                                                                             0.7006                                                                               -0.0480                                                                              -0.0228                                                                               0.1609                                                                               0.1817                                           __________________________________________________________________________

                                      Table 4                                      __________________________________________________________________________     (Embodiment 4)                                                                 Surface                                                                             Spherical                                                                            Coma  Astigmatism                                                                           Pepzval                                                                              Distortion                                            Aberration         Sum                                                    __________________________________________________________________________     A.sub.1                                                                             0.0003                                                                               0.0028                                                                               0.0226 0.0457                                                                               0.5595                                           A.sub.2                                                                             0.0015                                                                               -0.0119                                                                              0.0927 0.0156                                                                               -0.8443                                          A.sub.3                                                                             0.0183                                                                               0.0249                                                                               0.0338 0.2049                                                                               0.3241                                           A.sub.4                                                                             -2.0832                                                                              0.2333                                                                               -0.0261                                                                               -0.5403                                                                              0.0634                                           A.sub.5                                                                             0.4614                                                                               0.1710                                                                               0.0634 0.2350                                                                               0.1105                                           A.sub.6                                                                             -7.4566                                                                              0.9993                                                                               -0.1339                                                                               -0.6032                                                                              0.0988                                           B.sub.1                                                                             2.4826                                                                               0.4600                                                                               0.0851 0.1888                                                                               0.0507                                           B.sub.2                                                                             -2.2106                                                                              -0.4933                                                                              -0.1101                                                                               -0.1719                                                                              -0.0629                                          B.sub.3                                                                             6.9611                                                                               0.6517                                                                               0.0610 0.4186                                                                               0.0449                                           B.sub.4                                                                             0.4263                                                                               -0.2227                                                                              0.1163 0.0549                                                                               -0.0894                                          B.sub.5                                                                             0.1438                                                                               -0.1842                                                                              0.2361 0.0676                                                                               -0.3892                                          C.sub.1                                                                             -0.4874                                                                              0.3752                                                                               -0.2889                                                                               -0.1924                                                                              0.3705                                           C.sub.2                                                                             7.6340                                                                               -1.9869                                                                              0.5171 0.4703                                                                               -0.2570                                          C.sub.3                                                                             -10.3814                                                                             1.9754                                                                               -0.3759                                                                               -0.6937                                                                              0.2035                                           C.sub.4                                                                             -1.8167                                                                              -1.3323                                                                              -0.9770                                                                               -0.1698                                                                              -0.8410                                          C.sub.5                                                                             0.1333                                                                               0.2557                                                                               0.4902 -0.1615                                                                              0.6304                                           C.sub.6                                                                             2.4585                                                                               -0.4306                                                                              0.0754 0.5816                                                                               -0.1151                                          C.sub.7                                                                             0.0028                                                                               0.0085                                                                               0.0254 0.1084                                                                               0.4012                                           C.sub.8                                                                             4.3855                                                                               -0.4997                                                                              0.0570 0.2978                                                                               -0.0404                                          Σ                                                                             0.6736                                                                               -0.0044                                                                              -0.0359                                                                               0.1563                                                                               0.2182                                           __________________________________________________________________________

As is apparent from the aberration compensation shown in the aforesaid figures, the present invention presents a lens system having a wide field angle, a long back focus, a relative aperture presenting a high brightness and various aberrations well compensated.

Furthermore, according to the present invention, since the diameter of the lens on the object side may be maintained relatively smaller, the lens system may be used as a wide angle lens for a single reflex camera having the same threaded diameter for filters as that of the filters for the standard lens.

It will be understood that the above description is merely illustrative of preferred embodiments of the invention. Additional modifications and improvements utilizing the discoveries of the present invention can be readily anticipated by those skilled in the art from the present disclosure, and such modifications and improvements may fairly be presumed to be within the scope and purview of the invention as defined by the claims that follow. 

We claim:
 1. A retro-focus wide angle lens system comprising:a first component which is located on the object side, has a negative refractive power and consists consecutively from the front to the rear of a positive lens, a negative meniscus lens having a rear concave surface and a negative meniscus lens having a rear concave surface; a second component rearward of said first component and consisting from the front to the rear of a positive meniscus lens having a rear concave surface and a biconvex lens formed by a cemented doublet; a third component rearward of said second component and consisting consecutively from the front to the rear of a positive meniscus first lens having a rear convex surface, a biconcave second lens spaced from said positive meniscus first lens, a positive meniscus third lens having a convex rear surface and a positive fourth lens, said first and second lenses over-all having a negative refractive power; and a diaphragm disposed between said second and third components.
 2. A retro-focus type wide angle lens system comprisinga first component which is located on the object side, has a negative refractive power, includes a negative lens group having at least one negative meniscus lens; a second component rearward of said first component and including a lens group which has a positive refractive power and includes at least one biconvex lens; a third component rearward of said second component and consisting consecutively from the front to the rear of a positive meniscus first lens having a rear convex surface, a biconcave second lens, a positive meniscus third lens having a convex rear surface and a positive fourth lens, and satisfying the following conditions:

    (1) d.sub.c0 > d.sub.c2

    (2) | r.sub.c2 | ≧ | r.sub.c3 |

    (3) V.sub.c1 > V.sub.c2

    (4) d.sub.c0 > d.sub.c4

whereinr_(c2) and r_(c3) are the radius of curvature of the rear surface of the first lens of the third component and the radius of curvature of the front surface of the second lens of the third component, respectively; d_(c0) is the axial distance between the lens of the second component on the side nearest to the image and the first lens of the third component; d_(c2) and d_(c4) are the axial distance between the first and second lenses of the third component and the axial distance between the second lens and the third lens; and V_(c1) and V_(c2) are Abbe's Numbers of the first and second lenses of the third component,said lens system consisting of the following six lenses having a relative aperture of F/2.8, a back focus of 1.06 times the focal length and a field angle of 2ω = 64°:

    Radius of  Distance   Refractive Abbe's Number                                 curvature  along axis index                                                    ______________________________________                                         rA.sub.1 = 2.6542                                                                         dA.sub.1 = 0.057                                                                          NA.sub.1 = 1.5725                                                                         V.sub.A1 = 57.5                               rA.sub.2 = 0.5212                                                                         dB.sub.0 = 0.3292                                                   rB.sub.1 = 0.6639                                                                         dB.sub.1 = 0.2149                                                                         N.sub.B1 = 1.6968                                                                         V.sub.B1 = 55.6                               rB.sub.2 = -2.3966                                                                        dC.sub.0 = 0.1699                                                   rC.sub.1 = -0.9176                                                                        dC.sub.1 = 0.07                                                                           N.sub.C1 = 1.6583                                                                         V.sub.C1 = 58.5                               rC.sub.2 = -0.8435                                                                        dC.sub.2 = 0.1326                                                   rC.sub.3 = -0.4272                                                                        dC.sub.3 = 0.0439                                                                         N.sub.C2 = 1.7006                                                                         V.sub.C2 = 30.1                               rC.sub.4 = 2.5205                                                                         dC.sub.4 = 0.045                                                    rC.sub.5 = -1.8428                                                                        dC.sub.5 = 0.067                                                                          N.sub.C3 = 1.7305                                                                         V.sub.C3  = 54.4                              rC.sub.6 = -0.5054                                                                        dC.sub.6 = 0.0029                                                   rC.sub.7 = 5.8432                                                                         dC.sub.7 = 0.068                                                                          N.sub.C4 = 1.6775                                                                         V.sub.C4 = 55.5                               rC.sub.8 = -1.0495                                                                        Σd = 1.2004 .                                                 ______________________________________                                    


3. A retro-focus type lens system consisting of the following six lenses, having a relative aperture of F/2.8, a back focus of 1.06 times the focal length and a field angle of 2ω = 64°:Radius of Distance Refractive Abbe's Numbercurvature along axis index______________________________________rA₁ = 2.6542 dA₁ = 0.057 NA₁ = 1.5725 V_(A1) = 57.5rA₂ = 0.5212 dB₀ = 0.3292rB₁ = 0.6639 dB₁ = 0.2149 N_(B1) = 1.6968 V_(B1) = 55.6rB₂ = -2.3966 dC₀ = 0.1699rC₁ = -0.9176 dC₁ = 0.07 N_(C1) = 1.6583 V_(C1) = 58.5rC₂ = -0.8435 dC₂ = 0.1326rC₃ = -0.4272 dC₃ = 0.0439 N_(C2) = 1.7006 V_(C2) = 30.1rC₄ = 2.5205 dC₄ = 0.045rC₅ = -1.8428 dC₅ = 0.067 N_(C3) = 1.7305 V_(C3) = 54.4rC₆ = -0.5054 dC₆ = 0.0029rC₇ = 5.8432 dC₇ = 0.068 N_(C4) = 1.6775 V_(C4) = 55.5rC₈ = -1.0495 Σd = 1.2004 .______________________________________
 4. A retro-focus type lens system consisting of the following seven lenses, having a relative aperture of F/2.8, a back focus of 1.31 times the focal length and field angle of 2ω = 76°:Radius of Distance Refractive Abbe's Numbercurvature along axis index______________________________________rA1 = 0.9483 dA1 = 0.08 N_(A1) = 1.6214 V_(A1) = 61.3rA2 = 0.5452 dA2 = 0.17rA3 = 1.2630 dA3 = 0.065 N_(A2) = 1.6204 V_(A2) = 60.3rA4 = 0.5736 dB0 = 0.4145rB1 = 0.9542 dB1 = 0.31 N_(B1) = 1.7170 V_(B1) = 47.9rB2 = -1.8101 dC0 = 0.1401rC1 = -5.2127 dC1 = 0.0767 N_(C1) = 1.7440 V_(C1) = 44.9rC2 = -1.1791 dC2 = 0.0984rC3 = -0.6112 dC3 = 0.1467 N_(C2) = 1.7552 V_(C2) = 27.6rC4 = 1.7625 dC4 = 0.0304rC5 = -2.1584 dC5 = 0.085 N_(c3) = 1.7200 V_(C) 3 = 50.3rC6 = -0.5814 dC6 = 0.0032rC7 = 9.2635 dC7 = 0.07 N_(c4) = 1.6214 V_(C4) = 61.3rC8 = -1.8200 Σd = 1.69 .______________________________________
 5. A retro-focus lens system consisting of the following nine lenses, having a relative aperture of F/2.0, a back focus of 1.31 times the focal length and a field angle of 2ω = 76°.

    ______________________________________                                         Radius of  Distance   Refractive Abbe's Number                                 curvature  along axis index                                                    ______________________________________                                         rA1 = 2.6524                                                                              dA1 = 0.1030                                                                              NA.sub.1 = 1.6031                                                                         VA.sub.1  = 60.7                              rA2 = 0.7652                                                                              dA2 = 0.3086                                                        rA3 = 1.6973                                                                              dA3 = 0.1441                                                                              NA.sub.2 = 1.6668                                                                         VA.sub.2 = 33.1                               rA4 = -147.9947                                                                           dA4 = 0.04                                                          rA5 = 1.3048                                                                              dA5 = 0.0959                                                                              NA.sub.3 = 1.6890                                                                         VA.sub.3 49.3                                 rA6 = 0.5398                                                                              dB0 = 0.3153                                                        rB1 = 1.2986                                                                              dB1 = 0.2701                                                                              NB.sub.1 = 1.7050                                                                         VB.sub.1 = 54.8                               rB2 = -0.6026                                                                             dB2 = 0.1419                                                                              NB.sub.2 = 1.5190                                                                         VB.sub.2 = 57.3                               rB3 = -2.3600                                                                             dC0 = 0.1640                                                        rC1 = -1.2368                                                                             dC1 = 0.1100                                                                              NC.sub.1 = 1.5934                                                                         VC.sub.1 = 34.1                               rC2 = -0.8499                                                                             dC2 = 0.0862                                                        rC3 = -0.7622                                                                             dC3 = 0.1062                                                                              NC.sub.2 = 1.7847                                                                         VC.sub.2 = 25.7                               rC4 = 2.4184                                                                              dC4 = 0.0855                                                        rC5 = -1.8575                                                                             dC5 = 0.1007                                                                              NC.sub.3 = 1.7530                                                                         VC.sub.3 = 52.4                               rC6 = -0.7447                                                                             dC6 = 0.0067                                                        rC7 = 4.1620                                                                              dC7 = 0.1950                                                                              NC.sub.4 = 1.7050                                                                         VC.sub.4 = 54.8                               rC8 = 1.4574                                                                              Σd = 2.2729 .                                                 ______________________________________                                    


6. A retro-focus type lens system consisting of the following 10 lenses, having a relative aperture of F/2.0, a back focus of 1.31 times the focal length and a field angle of 2ω = 76°:Radius of Distance Refractive ABbe's Numbercurvature along axis index______________________________________rA1 = 8.9525 dA1 = 0.135 NA₁ = 1.6935 VA = 53.4rA2 =-26.3137 dA2 = 0.004rA 3 = 1.6630 dA3 = 0.06 NA₂ = 1.5168 VA₂ = 64.0rA4 = 0.6306 dA4 = 0.1152rA5 = 1.4500 dA5 = 0.06 NA₃ = 1.5168 VA₃ = 64.0rA6 = 0.5848 dB0 = 0.2622rB1 = 1.8044 dB1 = 0.06 NB₁ = 1.5168 VB₁ = 64.0rB2 = 1.9818 dB2 = 0.0704rB3 = 0.9816 dB3 = 0.2676 NB₂ = 1.6975 VB₂ = 48.2rB4 =-1.2300 dB4 = 0.094 NB₃ = 1.5231 VB₃ = 58.6rB5 =-5.0777 dC0 = 0.195rC1 =-1.9893 dC1 = 0.1097 NC₁ = 1.6200 VC₁ = 36.3rC2=-0.8138 dC3 = 0.086rC3 =-0.6430 dC3 = 0.1064 NC₂ = 1.8052 VC₂ = 25.4rC4 = 2.6269 dC4 = 0.05rC5 =-2.6680 dC5 = 0.1 NC₃ = 1.7570 VC₃ = 47.9rC6=-0.7408 dC6 = 0.0067rC7 = 3.8156 dC7 = 0.18 NC₄ = 1.7050 VC₄ = 54.8rC8 =-1.3884 Σd =1.9629 .______________________________________ 